A wide variety of implanted medical devices (IMDs) for delivering a therapy or monitoring a physiologic condition which can employ one or more elongated implantable medical electrical leads and/or sensors are available. Such IMDs can monitor or deliver therapy to the heart, muscle, nerve, brain, and stomach or other organs. Examples of such IMDs include implantable cardioverter defibrillator devices, which have a pulse generator and one or more electrical leads with one or more electrodes that conduct signals to and receive signals from the patient's heart. More recently, subcutaneous IMDs have been devised to deliver shocks to the heart by the use of a defibrillation lead placed subcutaneously on the torso.
These electrical leads and their electrodes are placed in or proximate to the organ such that an electrical signal between electrodes is capable of stimulating the organ. The electrodes may be configured either to deliver a stimulus to the organ, or to detect or sense an intrinsic electrical event associated with the organ. A programming device or programmer communicates with the medical device through a communication link. One example of a communication link is a telemetry link that provides means for commands and data to be non-invasively transmitted and received between the programmer and the device.
The electrical leads associated with IMDs typically include a lead body extending between a proximal lead end and a distal lead end and incorporate one or more exposed electrode or sensor elements located at or near the distal lead end. One or more elongated electrical conductors extend through the lead body from a connector assembly provided at a proximal lead end for connection with an associated IMD to an electrode located at the distal lead end or along a section of the lead body. Each electrical conductor is typically electrically isolated from other electrical conductors and is encased within an outer sheath insulator, which electrically insulates the lead conductors from body tissue and fluids. The leads can extend from a subcutaneous implantation site of the IMD through an internal body pathway to a desired tissue site. The leads are generally preferred having small diameter, highly flexible, reliable lead bodies that withstand degradation by body fluids and body movements that apply stress and strain to the lead body and the connections made to electrodes.
However, the conventional subcutaneous IMDs are incapable of delivering pacing therapies, such as anti-tachycardia pacing (ATP), without extreme discomfort to the patient. As such, the conventional subcutaneous IMDs are devised to deliver shocks to the heart by the use of a defibrillation lead placed subcutaneously on the torso. There remains a need in the art for improvements to the subcutaneous IMDs to provide a wide range of therapy delivery and sensing options.